An assistant principal shall be paid from state funds for ten months per year the amount for which he is eligible under Section 1305 (a) of this Title plus an annual amount for administrative responsibility to be determined in accordance with the following schedule and substitute in lieu the following:

Assistant principals in senior high schools, junior high schools and middle schools shall be paid from state funds for twelve months per year the amount for which they are eligible under Section 1305 (a) of this title plus an annual amount for administrative responsibility to be determined in accordance with the following schedule (elementary school assistant principals being paid from state funds for only ten months):